In automotive electronics, an electronic control unit (ECU) or control module is an embedded system that controls one or more of the electrical systems or subsystems in a vehicle. A typical ECU comprises a microcontroller unit (MCU) and an integrated power supply circuit comprising a voltage regulator. The power supply IC provides voltage Vdd and current to the MCU. The power supply IC may be part of a system base chip (SBC) also comprising other circuitry, such as other power supplies, local interconnect network (LIN) interfaces, controller area network (CAN) interfaces, voltage- and current-protection circuits, a watchdog for monitoring MCU operation, wake-up logic circuits, high side and/or low side switches, a logic state machine and so on. An ECU may have different modes of operation, such as a “normal”, “run” or “active” mode and a low power (LP) mode in order to reduce overall power consumption. Furthermore, an ultra-low power (ULP) mode may be available, where no output voltage and current is provided, only internal voltages are supplied and current consumption of the regulator is reduced to a minimum.
In “normal” mode, an MCU may be supplied with power and may be able to provide complete functionality. Its supply current may for example be in the range of ten to several hundreds of milliampere, with an internal current consumption of the power supply IC of a few milliampere (mA). In “normal” mode, a state-of-the-art power supply IC may be able to deliver some hundreds of milliampere, and at the same time provide a highly accurate voltage Vdd. In this mode, several protection schemes may be available, such as circuits for detecting and handling overcurrent, undervoltage, and overtemperature.
In a low power mode, the MCU may remain powered, however its current consumption may be reduced to some microampere (μA). In this mode, a connected power supply IC may also reduce its consumption to a value in a range of some microampere. In order to minimize current consumption, its protection schemes may also be disabled or reduced. In an automotive environment, the total system current consumption in low power mode may be a critical system parameter, as LP mode may be applied to the system, when the vehicle engine is turned off and therefore not recharges a battery of the vehicle supplying the current. The current consumed during LP mode of a state-of-the-art car ECU may, for example, be about 100 μA for a medium complexity ECU and about 500 μA for a very high complexity ECU. This standby current cannot be reduced to 0 A, since the power supply has to supply the MCU in the event of a wake-up.
The transition from LP mode to “normal” mode may be caused by a wake up event. The wake up event may be generated by different sources, for example by the power supply IC itself or by the MCU.
In an automotive environment, ECUs for car body applications may perform cyclic wake-up operations, that is an ECU may cyclically switch from LP mode to normal mode and check, whether or not an active state of the MCU is required and switch back to LP mode, when no wake-up is required. For example, an ECU controlling access to a car may determine each period of time T, whether or not the car is being opened using a key or a remote control. Therefore, the ECU may need to be awake for a time “t” during period T. Cyclic wake-up increases overall current consumption due to high consumption during time period “t”, therefore average consumption may be roughly proportional to “t”/T. During cyclic wake-up operation, state-of-the art circuits may switch from an LP mode to normal mode. Although the active time “t” may be short compared to cycle period T, operation in normal mode increases average current consumption. Furthermore, switching back from normal mode to LP mode may not be possible instantaneously, but may require additional transition time.
Since information, whether or not the system should stay in normal mode or return back to LP mode is available to the MCU, it may generally notify the power supply IC when to switch to another mode of operation. However, other methods relying on the evaluation of the load current may allow automatic transition from LP mode to normal mode as well.
Since transition from LP mode to normal mode may start after receiving a wake-up event notification from the MCU, a power supply IC may first enable protection schemes and enable its circuitry in order to deliver the full current to the MCU with the best output voltage accuracy. The MCU may for example use a serial peripheral interface (SPI) bus for sending SPI commands to the power supply IC.